Ultra high frequency converter of the space-resonant type



April 8, 1947- E. D. MCARTHUR ULTRA HIGH FREQUENCY CONVERTER OF THE SPACE-RESONANT TYPE Filed March 2d, 1943 2 Sheets-Sheet 1 nnnn CIRCUIT Inventor:

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April 1947- E. D. MCARTHUR 2,418,518

ULTRA HIGH FREQUENCY CONVERTER OF THE SPACE-RESONANT TYPE Filed March 20, 1-945 2 She ets-Sheet 2 CIRCUIT Inventor: Elmer D. Mc Arthur,

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Patented Apr. 8, 1947 ULTRA HIGH FREQUENCY CONVERTER OF THE SPACE-RESONANT TYPE Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 20, 1943, Serial No. 479,926

14 Claims.

My invention relates to ultra high frequency systems and more particularly to ultra high frequency converters of the space-resonant type.

It is an object of my invention to provide a new and improved ultra high frequency system.

It is an other object of my invention to provide a new and improved ultra high frequency converter of the space resonant type.

It is a further object of my invention to provide new and improved structure for an ultra high frequency conversion system which may be employed as a signal comparison means.

It is a still further object of my invention to provide new and improved methods of operating a space resonant system which comprises an electric discharge device.

Briefly stated, in the illustrated embodiment of my invention I provide a new and improved ultra high frequency space resonant system, which may be employed as a converter or as a signal converter or comparison means, whereby differences in electrical characteristics of two high frequency signals may be readily compared. A conductive member, such as a hollow cylinder, defines in part a space resonant cavity and houses an electric discharge device including a plurality of longitudinally disposed electrodes including an anode, a cathode and a grid, the cathode being electrically connected to the cylinder. A second conductive member, such as a metallic cylinder, is placed within the first cylinder and is electrically connected to the grid of the discharge device, and defines with the inner surface of the first cylinder a space resonant region or. cavity which is of tunable or controllable character.

A plurality of excitation means are associated with the cavity and may include a pair of Iongitudinally positioned input electrode means physically displaced from the electric discharge device, and which serve to establish within the space resonant cavity excitations due to signal voltages which are to be utilized or compared. Where the signals are of the same order of magnitude and of substantially similar frequency, the input electrode means for one type of operation of my device may be positioned apart by a distance corresponding to an odd multiple of a half wave length corresponding to the natural frequency of the space resonant region, or corresponding to the excitation produced by one of the input electrode means. By such an arrangement of elements, the transit time of the electromagnetic energization between the input electrode means and the grid-cathode circuit of the discharge device serves to produce across the in- 2 put electrodes of the discharge device a net or resultant excitation which controls the discharge device to produce across the anode and cathode thereof voltage differences corresponding to such net or resultant excitation. If the two input signals are of the same magnitude and phase, no resultant high frequency voltage appears across the anode and cathode. is a difference in either phase or magnitude, a resultant high frequency voltage appears thereacross. suitable external circuit means comprising a circuit tuned to either the sum or the difference of the frequencies of excitation for utilization or signalling purposes.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. 1 is a cross-sectional view of an ultra high frequency space resonant system built in accordance with my invention, and. Fig. 2 is a detailed view of one type of high frequency electric discharge device with peculiarly adapted,

high frequency terminals which may be employed in the system. Fig. 3 illustrates a modification of the arrangement shown in Fig. 1 applied to a heterodyne system.

Referring now to Fig, 1 of the drawing, my invention is there illustrated as applied to an ultra high frequency space resonant system comprising in part a conductive member or hollow cylinder I which may be constructed of a high conductivity metal. Within the cylinder I, I pro-.

vide electric discharge device 2, details of which are shown in Fig. 2. The discharge device shown in Fig. 2 is of the type peculiarly adapted for the utilization of ultra high frequency energy and comprises a solid metallic anode cylinder 3, a hollow cathode cylinder 4 having a closed end 5 facing the anode 3 and upon which there is placed a suitable electron emissive material such as barium oxide or the like. Interspaced between the anode 3 and cathode 4 there is provided a grid 6. The above described electrodes of the discharge device may be supported in a manner disclosed and claimed in a copending patent application Serial No. 436,633 of James E. Beggs. filed March 28, 1942, and which is assigned to the assignee of the present application. More particularly, the electrodes may be supported in the desired spaced relation by means of a series of tapered metallic disks 1, 8 and 9 progressively increasing in diameter in the order named, and which constitute in part the enclosing envelope If there This resultant voltage may be utilized by for the electrodes. Vitreous cylinders I and II are sealed in end-to-end relation with respect to disks I, 8 and 9, thereby defining an additional enclosure constituting part of the sealed enveiope for the discharge device. Anode 3 extends through an aperture in disk I and is sealed to the disk, and may be provided with an enlarged upper section I2 which constitutes an anode connection for the device.

Disk 9 may be provided with a flange 53 which is supported by a base It. The cathode cylinder 4 is in turn provided with a flange I5 which parallels the under surface of disk 9 and is maintained in insulated relation with respect thereto by means of an annular insulating washer I6. By virtue of the washer I6, the cathode structure is insulated from disk 9, so far as unidirectional potentials are concerned, but due to the mutual capacitance between disk 9 and flange I5 there is provided an eiiective high frequency coupling between these elements. Unidirectional potential may be applied to the cathode cylinder 4 through conductors [l and I8 which are connected to terminal posts it and supported by base la. The cathode structure is provided with a centrally located filamentary or spiral heating element 2| which is connected to externally accessibl'e terminal posts 22 and 23 through leadinwires 24 and 25.

Returning now to" the space resonant system shown in Fig. l, the electric discharge device 2 is supported in the position illustrated so that the electrodes'of the device assume longitudinally displaced positions, and the discharge device 2 may be seated in a socket 26 provided with terminals 21-30, inclusive, which are connected to terminal posts I9, 20, 22 and 23, respectively, 'of the discharge device. The socket 2B, and hence the electric discharge device 2, may be held in the illustrated position by means of annular members 31 and 32, the former of which, in turn, is seated against an appropriately formed shoulder of a cylinder 33 which telescopes one end of cylinder I. The two cylinders I and 33 may be joined by means of a thread collar 35 adapted to receive threads at this end of cylinder I. The cathode of discharge device 2 is electrically connected to the'metallic cylinder I by suitable connecting means, such as a plurality of annularly spaced resilient'fingers 35 supported by a metallic ring 36,-th'ereby constituting one part of the electrical connections for the input circuit to discharge device 2.

Within cylinder I I provide a second conductive means such as a hollow metallic cylinder 31, which is in spaced relation with respect to the inner surface of cylinder I and which defines with this surface a space resonant region or cavity, the natural frequency of which is controlled'by suitable'tuning means such as an annular longitudinally adjustable plunger 38. Plunger 38 may be adjusted in its longitudinal position by a suitable mechanical expedient such as rods 39, and theplun'ger 38 1s arranged to engage closely the outer'surface of cylinder sl and the inner surface of cylinder I. Cylinder 3'! may be maintained in the desired spaced relation by means of an end ring 40 which fits into one end of cylinder I.

Cylinder 31 is electrically connected to grid disk 8 by suitable electrical connections such as a plurality of annularly spaced resilient fingers which are welded or soldered to one end of cylinder 31; These fingers are' adapted to engage a face 'ofdisk 8 and. toassurne the stressed curvature shown upon insertion of the electric dis- 4 charge device in the illustrated position, thereby assuring positive electrical contact between the grid disk 8 and cylinder 3?.

An externally accessible electrical connection for the anode of the discharge device 2 may be provided by means of a longitudinal connector 2 adapted to engage the anode extension I2 and which extends through cylinder 3'3. Unidirectional potential may be impressed across the anode and the cathode of discharge device 2 by applying a positive potential to connector rod 42 and a negative potential to either terminal 21 or 28 a of the socket 26. r y

In order to establish a plurality, such as two, excitations within the space resonant cavity, I provide a pair of longitudinally positioned excitation means each of which comprises an electrode means. For example, for this purpose I may employ a pair of input electrode means comprising conductors 53 and M, for establishing excitations within the space resonant region defined between the outer surface of cylinder 3''! and the inner surface of cylinder i. The electrode means or conductors i3 and M may constitute extensions of inner conductors 45 and 36 of concentric transmission lines comprising said inner conductors and outer metallic tubular conductors 51 and 48.

Atleast one of the above described input electrode means or excitation means may be positioned longitudinally in order to match the resistance of the cavity to the resistance of the input transmission lines. For example, the input electrode means comprising conductor 43 may be electrically connected by a welding or soldering process to the outer surface of cylinder 31 at a point which establishes the desired equality between the resistance of the transmission line and the resistance of the cavity.

Where it is desired to use my invention as a signal generator or as a means for detecting differences in phase or magnitudes of two input signals, the electrode means or excitation means may be positioned longitudinally at a distance corresponding to an odd number of multiples of a half wave length of the natural frequency of the space resonant cavity, or an odd number of multiples of a half wave length of one input excitation frequency. For example, if the Wave length corresponding to the natural frequency of the space resonant cavity is represented by the symbol A, the distance between the conductors 45 and 45 may be i As a means for further tuning the impedances of the input transmission lines to the impedance of the cavity, the concentric transmission lines may be provided with tuning plungers t9 and at which are adjustable vertically along the inner'surfaces' of tubular conductors ll and 48. The high frequency potentials produced across the anode and, the cathode of the discharge device 2 may be utilized externally by means of av suitable intermediate frequency circuit connected to the anode connector 42.

In explaining the operation of the embodiment of my invention shown in Fig. 1, it will be considered that a unidirectional potential is applied across the anode and cathode of the discharge device 2 and that the plunger 38 is adjusted to establish or tune the space, resonant cavity to have 'a predetermined frequency correlated to the frequency of excitation produced by one of the electrode means, such as above described conductor 53 and conductor 41. For example, the plunger 38 may be adjusted to assume a longitudinal position corresponding to an odd multiple of quarter wave lengths of the excitation which is supplied by the conductor :13.

Upon the establishment of a second excitation within the cavity by means of conductors 44 and 48, if the phase and magnitudes of these two excitations are equal, due to the transit time of the electromagnetic energization incident to conductor 44, there will be substantially no high frequency potential difference impressed across the grid and cathode of electric discharge device 2, the excitation incident to conductor 44, due to transit time in traveling the distance arriving in exact time phase opposition with that due to conductor 53. Consequently, when the two signals are of equal magnitude and of the same phase, there will be no high frequency potential difierence across the anode and cathode of discharge device 2. However, upon any deviation in phase relation or upon change in the respective magnitudes of the incoming signals, the net or resultant excitation impressed across the grid and cathode of discharge device 2 will assume a definite value, or number of values, corresponding to the sum and the difierence of the two excitations. These differences of potential serve to modulate the electron stream of the discharge device producing corresponding heterodyned differences of potential across the anode and cathode of the discharge device which may be utilized in an external circuit, such as a tuned intermediate frequency circuit connected to anode rod 62.

As stated above, the input electrode means, such as either conductor d3 or Lid, may be positioned at a point so that the resistance of the cavity is equal to the resistance of the associated transmission line, thereby establishing that condition necessary for maximum power transfer between the transmission line and the cavity. As presupposed above, due to the adjustment of tuning plunger 38 to establish the desired natural frequency of the cavity, the cavity may have a definite reactive component, either inductive or capacitive. exact matching between the impedance of the transmission line and the impedance of the cavity, it is necessary that these complex impedances have a conjugate relationship; that is, if the reactance of one is inductive the reactance of the other should be capacitive. This relationship between the respective reactances of the transmission line and the cavity may be obtained by the joint control of the positions of plunger 38 and either plunger 59 or 58.

Fig. 3 illustrates a further modification of my invention which is similar in many respects to that shown in Fig. 1; and corresponding elements have been assigned like reference numerals. The system of Fig. 3 is of the heterodyne type wherein an excitation is established within the space resonant cavity, at local oscillator frequency, by means of electrode means such as a loop 5i which comprises an extension of an inner conductor of a concentric transmission line 52 comprising an outer tubular conductor 53 and an inner conductor 54. The transmission line 52 may be supported by plunger 38.

Employing the above described general type of control or detection for incoming signals, I

In order to establish 6 provide within the space resonant cavity a pair of electrode means, such as disks 55 and 56, in proximity to but physically displaced from the outer surface of cylinder 31. The disks 55 and 55 are preferably spaced a half wave length of the signal excitation, or odd multiples thereof, and are respectively energized from concentric transmission lines 5? and 53 comprising outer tubular conductors 59 and 65 and inner conductors BI and 52, respectively.

In order to obtain optimum matching of the impedances of the transmission lines 51 and 58 with the respective associated impedances of the cavity, I provide means for adjusting the position of the input electrode means comprising disks 55 and 56 within the cavity and means for controlling the impedances of the transmission lines.

As a means for controlling the positions, particularly the axial positions, of the input electrode means and the transmission lines 5'! and 58, I employ a suitable mechanical expedient such as a thumbscrew adjusting means 53 which is mechanically connected to a metallic plate 64 into which conductor Ell extends, the former being in electrical contact with and slideable on cylinder I. In like manner, conductor 59 is supported by an adjustable plate 55 which is in slideable engagement with the outer surface of cylinder l to permit axial movement of its associated input electrode means. As a further means for controlling the distance between the input electrode means comprising disks 55 and 56, I provide a further mechanical adjusting means 65 which may include a pair of rods 6'! and 63 provided at facing extremities with left-hand and right-hand screwthreads, respectively, or vice versa, and a threaded adjusting sleeve 69.

In order to tune the impedance of one of the transmission lines, such as transmission line 58, this line may be provided with a T-shaped tuning arrangement 70 comprising an outer tubular conductor II and a positionable tunin plunger 12. If desired, the transmission line 57 may also be provided with a similar or equivalent tuning means.

The operation of the embodiment of my invention shown in Fig. 3 will be explained by considering the system when a local oscillator excitation of predetermined frequency is established within the space resonant cavity by energizing transmission line 52 from a local oscillator (not shown). Upon the energization of transmission lines 51 and 58 from separate sources having substantially the same frequency, and upon adjusting the input electrode means to be substantially a half wave length or an odd multiple thereof apart, an intermediate frequency circuit connected to the anode-cathode circuit of discharge device 2 will be energized in accordance with a resultant of the input excitations and the local oscillator excitation; that is, the system is heterodyned. If there is substantial phase coincidence between the input excitations derived from transmission lines 5i and 5B, and if the excitations are of the same magnitude, the net excitation impressed on the grid-cathode circuit of discharge device 2, due to these two excitations, will be zero in accordance with the principles explained above. The local oscillator frequency is then the only eiTective frequency present so far as the cathodegrid circuit of the discharge device 2 is concerned, and only a high frequency component of voltage corresponding to the local oscillator frequency will appear across the anode and cathode ofthe dis- 7 charge device. Inasmuch as the intermediatefrequency circuit connected to the anode is tuned to the intermediatefrequency and since this circuit will have a relatively low impedance to currents of local oscillator frequency, substantially no voltage will be produced in the intermediate frequency circuit. However, upon variation in relative magnitudes of the input excitations from transmission lines and 58, or variation in phase of these two excitations, there will be impressed across thegrid and cathode of discharge device 2 an excitation which is a resultant of these two excitations and the local oscillator excitation. Consequently, a corresponding high frequency voltage having components equal to the sum and the difference of the net input excitation and the local oscillator excitation will appear across the anode and cathode of discharge device 2, producing a voltage in theutilization or intermediate frequency circuit which is tuned to one of these component voltages.

The impedances of transmission lines 51 and .58 may be tuned or matched to the respective cavity impedances associated with each of the input electrode means or disks 55 and 56. This matching of impedances may be accomplished by auxiliary tuning means such as element 10 and corresponding means associated with transmission line 51, or by the proper design of the impedances of transmission lines 5'! and 58 with respect to cavity impedances for given positions of the input I as applied to space resonant cavities of particular form and as embodying various particular devices, it will be obvious to those skilled in'the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1.'In an ultra high frequency space resonant system, the combination comprising a space resonant region defined by a conductive 'member, an electric discharge device located within said member and comprising a plurality of enclosed electrodes including a cathode, a grid and an anode having externally accessible high frequency terminals and positioned in longitudinal spaced relationship Within said member, a conductive member within said first mentioned member electrically connected to the grid terminal, means for connecting said cathode to the first mentioned member, means for tuning the space be tween said member and said second mentioned member, input electrode means extending into the space defined by said members to establish excitation of said space at a predetermined frequency, and second electrode means longitudinal- 1y positioned from the first mentioned electrode means for establishing a second excitation of said space whereby the grid-cathode circuitof saiddischargedevice is excited in accordance with a'resultant of the two excitations thereby 8 producing a corresponding potential difference across saidanode and saidcathode.

2. In an ultrahigh frequency converterof the space resonant type, the combination comprising a hollow conductive member, an electric discharge device within said member including a plurality of electrodes comprising a cathode, a grid and an anode provided With externally accessible high frequency terminals, a second conductive member within the first member and electrically connected to said grid terminal for defining with the first mentioned member a space resonant cavity, means for connecting said cathode to the first mentioned member, means for tuning said cavity, input electrodemeans associated with said cavity and longitudinally displaced from said discharge device for establishing excitation of said cavity at substantially its naturalfrequency, and means for modulating the grid-cathode excitation of said discharge device comprising a second electrode means longitudinally displaced from the first electrode means whereby the transit time incident to the differ ence in longitudinal displacements between the two electrode means and the discharge device is utilized for the purpose of detecting differences in phase and magnitudes of the cavit excitations.

3. In an ultra high frequency converter of the space resonant type, the combination comprising a hollow conductive member, an electric discharge device including a plurality of enclosed electrodes comprising an anode, a cathode and a grid provided with externally accessible high frequency terminals, a second conductive member within the first mentioned member and electrically connected to said grid for defining with the first mentioned member a space resonant cavity, means for connecting said cathode to the first mentioned member, means for tuning said cavity, a first input electrode means for establishing an excitation of predetermined frequency within said cavity, and a second electrode means longitudinally displaced from the first electrode means a distance corresponding to an odd multiple of a half Wave length of the natural frequenc of said cavity thereby establishing acros the anode and cathode of said discharge device a potential difference which is a function of the relative magnitudes and phase of the signal voltages applied to said first and said second electrode means.

4. In an ultra high frequency space resonant system, the combination comprising a space resonant region defined'by a conductive member, an electric discharge device located within said member and comprising a plurality of enclosed electrodes including an anode, a cathode and a grid having externall accessible high frequency terminals, a conductive cylinder within said member electrically connected to the terminal associated with said grid, means for tuning the space between said member and said cylinder, input electrode means connected tosaid cylinder, second input electrode means connected to said cylinder at a distance from the first of said input electrode means corresponding to an odd multiple of a half wave length of the natural frequency of said region, and means connected to said anode and said cathode for the utilization of a component of anode-cathode voltage dependent upon the net excitation of said cavity. 1

5. In an ultra high frequency signal converter of the space resonant type comprising a'member ofconductive character, an electric discharge de- 9 vice within said member including a plurality of enclosed electrodes comprising an anode, a cathode and a grid provided with externall accessible high frequency terminals, a conductive cylinder within said member and electrically connected to the grid terminal for defining with said member a space resonant cavity, electrode means connected to said cylinder for establishing a first excitation Within said cavity, second electrode means connected to said cylinder and displaced longitudinally from the first mentioned electrode meanslat a distance corresponding to a multiple of a half wave length of the natural frequency of said cavity, means for tuning said cavity, and means connected to said anode and said cathode energized in accordance with a resultant of the net excitations produced by the first mentioned and said second electrode means.

6. In an ultra high frequency space resonant signal converter, the combination comprising a hollow conductive member, an electric discharge device within said member comprising a plurality of enclosed electrodes including an anode, a oathode and a grid and provided with externally accessible-high frequency terminals, a second conductive member within said first mentioned member and electrically connected to said grid defining with thefirst mentioned member a space resonant region, afirst elect ode means extending into said region for establishing an excitation of predeterminedfrequency therein, a second electrode means spaced longitudinally from the first mentioned electrode means at a distance corresponding to a multiple of a half Wave length of the natural frequency of said space resonant region, and utilization means connected to said anode and said cathode and responsive to a resultant of the excitations produced by said first and second electrode means.

7. In an ultra high frequency converter of the space resonant type, the combination comprising a hollow conductive member, an electric discharge device within said member including a plurality of electrodes comprising a cathode, a grid and an anode provided with externally accessible high frequency terminals, a second conductive member within the first member and electrically connected to said grid terminal for defining with the first mentioned member a space resonant cavity, means for connecting said cathode to the first mentioned member, means for tuning said cavity, input electrode means associated with said cavity and longitudinally displaced from said discharge device for establishing excitation of said cavity at substantially its natural frequency, and means for modulating the net excitation appearing across said cathode and said grid comprising a second electrode means longitudinally spaced from the first mentioned electrode means by a distance corresponding to a half wave length of the cavity frequency whereby the net gridcathode excitation is employed to produce across the anode and the cathode electrical variations incident to differences in phase and magnitude of the two excitations.

8. In an ultra high frequency converter of the space resonant type, the combination comprising a hollow conductive member, an electric discharge device including a plurality of enclosed electrodes comprising an anode, a cathode and a grid provided with externally accessible high frequency terminals, a second conductive member within the first mentioned member and electrically connected to said grid for defining with the first mentioned member a space resonant cavity, means for connecting said cathode tothe first menspace resonant type, the combination comprising a hollow conductive member, an electric discharge device including a plurality of enclosed electrodes comprising an anode, a cathode and a grid provided with externally accessible high frequency terminals, a second conductive member within the first mentioned member and electrically connected to said grid. for defining with the first mentioned member a space resonant cavity, means for connecting said cathode to the first mentioned member, means for tuning said cavity, a pair of adjustable input electrode means for establishing an excitation of predetermined frequency within said cavity, said input electrode means being longitudinally displaced from said discharge device, and means for establishing an excitation of predetermined frequency within said cavity whereby upon deviations in .relativephase or magnitude of the input signals applied to said pair of electrode means an intermediate frequency potential difference is produced across said anode and said cathode.

10. In an ultra high frequency converter of the space resonant type the combination comprising a, hollow conductive member, an electric discharge device including a plurality of enclosed electrodes comprising an anode, a cathode and a grid provided with externally accessible high frequency terminals, a second conductive member within the first mentioned member and electrically connected to said grid for defining with the first mentioned member a space resonant cavity, means for connecting said cathode to the first mentioned member, means for tuning said cavity, a pair of displaced input electrode means for establishing an excitation of predetermined frequency within said cavity, said input electrode means being longitudinally displaced from said discharge device, means for adjusting the distance between said pair of input electrode means to correspond to a half wave length of the electrode means excitation, means for establishing local oscillator excitation within said cavity, and intermediate frequency utilization means connected to said anode and said cathode.

11. In an ultra high frequency converter of the space resonant type, the combination comprising a hollow conductive member, an electric discharge device including a plurality of enclosed electrodes comprising an anode, a cathode and a grid provided with externally accessible high frequency terminals, a second conductive member within the first mentioned member and electrically connected to said grid for defining with the first mentioned member a space resonant cavity, means for connecting said cathode to the first mentioned member, means for tuning said cavity, a pair of concentric transmission lines terminated in a, pair of electrode means extending into said cavity, said electrode means being longitudinally displaced within said cavity from said discharge device, means for concurrently controlling the 11. osition 'of' said electrode means withinsaid:- cavity, and means for adjusting-the spacing between said pair of electrode means.

12. In an ultra high frequency converter of the space resonant type, the combination comprising a hollow Conductive member defining a space resonant cavity, an electric discharge'device within said cavity having a, grid-cathode circuit energized in response to the net excitation of said cavity, 1neans'for establishing excitations within said cavity; said means being spaced from said device by a distance substantially equal to a half Wave-length of the mean frequency of the excitations, means'for establishingwithin said cavity an excitation of substantially constant frequency, and means for utilizing the intermediate frequency potential appearing across the anode and cathode of said discharge device.

13L The method ofutilizing a space resonant cavity'for Wave comparison purposes which com prisesestablishing an electric discharge at a point within said cavity, establishing a predetermined excitation ofsaid cavity of one frequency at a first" position within said cavity, establishing a second excitation of substanti'allythe same frequency within said cavity'at a position displaced from the first position by' adistance corresponding to substantially a half wave length at said frequency thereby utilizing the time of transit of the electromagnetic energization of said cavity between said excitations and said discharge for controlling the phase and magnitude of the resultant voltage-impressed across a portiorr'of said discharge, and utilizing the net excitationnof said cavity for producing a, corresponding potential difference across said discharge.

14. The method of comparing ultra high fre-' quency waves in a space resonant cavity which comprises applying a unidirectional voltage across a portion of said cavity to establish an electric discharge, exciting said cavity at a frequency, corresponding to the natural frequency of said cavity and at aposition displaced from said discharge, and establishing a, second'excitation in said cavity at a position displaced from said first excitation by a distance corresponding to a' half wave length of the first excitation whereby the net excitation impressed across said discharge serves to detect differences in phase and magnitude of said two excitations.

ELMER D, MCARTHUR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

